Passive Solar 101

There is nothing complicated about passive solar. When the sun beats down on the top of your head, that’s passive solar. When the sun pours through your window and your cat luxuriates in its warmth, that’s passive solar. When your car is broiling hot after a few hours in a hot parking lot, that’s passive solar.

Harnessing passive solar is the tricky part. A house that relies on passive solar for most of its heating and cooling needs does so without the benefit of mechanical equipment. Very few houses can achieve 100 percent passive solar success, but many can grab the sun for some significant help.

Passive Solar in GeneralIt’s easiest to apply passive solar design techniques to new construction, but even older buildings and additions can take advantage of it.

Essentially, the location of the windows and how they are glazed contributes to its efficacy. Windows should be well sealed and insulated. South-facing windows are the best for heat and light.

When cooling the house is the primary concern, north-facing windows and well-shaded south-facing windows are preferred.

Your home’s comfort will further be determined by how well insulated it is. Tightly sealed windows, moisture control (dehumidifiers, for instance) and good ventilation help, too.

Ventilation can be achieved with the use of fans and ducts, exhaust fans in strategic places, and of course through unavoidable ways, such as open windows, cracks in the walls, and doors that don’t fit properly. Not surprisingly, the last method is not highly recommended.

Utilizing Passive Solar When You BuildThe kind of material used to construct a building can affect how solar energy is used. Some materials reflect the sun, while others absorb it. Choose yours depending on where you live and how you intend to use solar energy.

Heat produced by the sun also causes air to move and a clever design can take advantage of this. Hot air can be directed in or out of a building.

How a house is sited is critical to making the most of passive solar. Its south side should receive sunlight during the optimal sunlight hours — usually between 9 a.m. and 3 p.m. to take advantage of the sun’s heat. Situate most used living areas along the south side of the dwelling, too, and those used least along the north side. An open floor plan is the most efficient for passive solar systems.

In the warm months, rely on shading over the windows to keep the sun, when it’s highest in the sky, from beating through the windows. These may be overhangs or blinds. When the sun is low in the winter sky, overhangs will let sunlight into the house. In the summer, when it’s high in the sky, they will keep it out. Good glass in the windows helps immeasurably, too, of course.

Visualize traditional houses in desert regions, built before central heat and air. They have thick walls and deep-set windows, designed to make the best use of passive solar. The thick adobe or stone walls have good thermal mass that holds in the heat of day to warm the house at night, and then holds in the cool of the night to keep the interior comfortable during the day. The deep-set windows essentially are well shaded.

Most of us depend on passive solar heat without thinking about it. Harnessing the sun to help cool a house, or to heat water for a pool, for instance, is a job for experts.

Enjoy the sun while it shines!

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